Efavirenz is an essential component of HIV treatment in children aged 3 years or older on anti-tuberculosis (anti-TB) treatment. However, the appropriate efavirenz dose during anti-TB treatment remains unclear. Rifampin (an anti-TB drug) increases the activity of the drug metabolizing enzymes that breakdown efavirenz, which may lead to low blood levels of efavirenz and treatment failure during cotreatment. The drug-to-drug interactions between the HIV and anti-TB drugs also vary between individuals based on genetic factors. This study will investigate the effects of anti-TB treatment, as well as drug-gene interactions on the blood concentrations of efavirenz in children with HIV and TB infections. Such data could enhance optimization of efavirenz dosage or selection of alternate regimens in some children.

Area under time curve from time 0-24 hours(AUC0-24h) of efavirenz [ Time Frame: At week of 4 of HIV therapy ] [ Designated as safety issue: No ]

Compare efavirenz AUC0-24h between HIV-infected children without TB and those with TB on rifampin-containing anti-TB therapy in co-infected patients

Secondary Outcome Measures:

Number of children with grade 3 or 4 liver enzymes elevations compared to baseline, new onset of skin rash, nausea, vomiting or treatment modification due to drug side effects [ Time Frame: up to week 24 of therapy ] [ Designated as safety issue: Yes ]

Compare frequency of adverse events as a measure of safety and tolerability between HIV-infected children with and without TB coinfection

Number of children with efavirenz 24-hour post-dose concentration (C24h) < 1000 ng/mL [ Time Frame: At week 4 of therapy ] [ Designated as safety issue: No ]

Relationship between clinical factors (weight, gender, nutritional status) as well as genetic factors (CYP2B6 516G>T, as well as CYP3A4, ABCB1, CAR and PXR polymorphisms) and efavirenz AUC0-24h and efavirenz C24h will be investigated

Number of children who discontinue efavirenz therapy due to drug side effects [ Time Frame: Up to week 24 of HIV therapy ] [ Designated as safety issue: Yes ]

Relationship between clinical factors (weight, gender, nutritional status) as well as genetic factors (CYP2B6 polymorphisms) and treatment modification due to drug side effects in the combined study population

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Please refer to this study by its ClinicalTrials.gov identifier: NCT01704144